226 Geological Society : — 



of succession. They appear at Castle Cornet to meet the gneiss 

 intrusively, and their microscopic structure is igneous. A remark- 

 able appearance of bedded structure at Port Doyle is the only 

 strong argument for a metamorphic origin, and this may be ex- 

 plained as a caught-up mass in conjunction with crushing-planes. 

 The author therefore regards them as igneous. 



An oval area between St. Sampsons and St. Peter's Port is occu- 

 pied by hornblendic rocks, locally called " birdseye," which may be 

 described as hornblende-gabbros. These also have been called meta- 

 morphic. They too, at Hogue-a-la-Perre and at another point, present 

 appearances of bedding ; but on the same general grounds as for 

 the preceding group, these also are regarded as igneous. 



Two granitic masses are described : the coarse pink granite of 

 Cobo, on the west coast, and the finer-grained grey granite weather- 

 ing pink of Lancresse, on the north. Each is seen to intrude : the 

 Cobo granite into gneiss at Hommet Barracks ; the Lancresse granite 

 into diorite at Port Le Marchant. Besides these are some smaller 

 masses. 



Dykes are remarkably abundant and various. Granites and elvans 

 are plentiful everywhere ; felsites very rare. The majority of the 

 dykes are diorites, varying in coarseness and often of enormous 

 size ; there is also mica-trap. In some of these dykes a cleavage 

 has been developed, so that some resemble slates. Infiltration- veins 

 are abundant. 



In relative age the gneiss appears to be the oldest rock, the 

 hornblende-gabbro to be next, then comes the diorite group, while 

 the granites are newer still. Of the dykes the newest are the com- 

 pactest diorites. As to the absolute geological age of the rocks 

 no satisfactory evidence at present is known ; it will have to be 

 sought for in the other islands and in Prance. 



2. " On anew specimen of Megcdichthys from the Yorkshire Coal- 

 field." By Prof. L. C. Miall, P.G.S. 



3. " Studies on some Japanese Pocks." By Dr. Bundjiro Koto. 

 Communicated by Prank Iiutley, Esq., P.G.S. 



The author has studied series of Japanese rocks from the collec- 

 tion of the Tokio University and the Geological Survey of Japan. 

 The microscopical investigation was carried on at the Mineralogical 

 Institute of Leipsic, under the direction of Prof. Zirkel, and the 

 chemical analyses were made in the laboratory of Prof. Knop. 



The most abundant rocks are the pyroxene-andesites, which are 

 not of a glassy texture, but for the most part holocrystalline. The 

 most abundant mineral in these rocks is a plagioclase felspar with 

 twinned and zonal structure, which is proved by its extinction- 

 angles and by the chemical analysis of its isolated fragments, to be 

 labradorite. Sanidine is present in small quantities. 



The augites of these rocks present many peculiarities ; they are 

 all decidedly pleochroic ; and they exhibit the oblique extinction in 



